Business, science and entertainment applications depend upon computers to process and record data, often with large volumes of the data being stored or transferred to removable media. The removable media typically take the form of a magnetic tape cartridge, an optical disk cartridge, floppy diskettes, or floptical diskettes. The advantages of storing data on removable media are numerous, including: a capability of storing hundreds of megabytes or even gigabytes of data (additional cartridges can be used to store still more data); providing a vehicle for long term storage and archival; backing up that data which resides on non-removable media; and providing a convenient vehicle for transferring data between computers. Typically, removable media is the most economical means of storing or archiving the data.
In the past, when a request for a specific removable data cassette (or tape reel) was issued, an operator needed to retrieve the data cassette and physically load that cassette into the storage device. This manual mode suffered a significant delay while the cassette was being retrieved by the operator before the data on that cassette could be processed. Unfortunately, the operator could easily make an error retrieving and loading an incorrect cassette.
With advancements in data storage products, the data cassettes were reduced in size while increasing an amount of data storage capability and robots were designed and incorporated to automatically retrieve cassettes and load those cassettes into a storage device. The robot is housed within an automated storage library that also contained one or more storage devices and a plurality of cassettes placed within storage cells. Still more convenience was provided by using removable magazines, each having a plurality of storage cells for loading and unloading many data cassettes at a time. The robot replaced the operator and improvements were seen in access time and in reliability. However, because the robot is a complex machine requiring multiple degrees of freedom (rotation and translation about the mechanical joints) it would require maintenance and adjustments. The robot's complexity also resulted in a significant increase in manufacturing and maintenance costs.
The difficulties that exist with the multiple degrees of freedom within a robot have been addressed, to some degree, by using a pass-through picker. The pass-through picker is the assembly that retrieves a cassette from a storage cell and places the cassette into the storage device. The pass-through picker assembly is positioned within an automated storage subsystem between the storage device and the storage cells. The storage cells are typically located parallel to and opposite the storage device(s). The pass-through picker retrieves a cassette from the storage cell, passes the cassette through its structure, and transfers the cassette to the storage device. This reduces the complexity of the picker as compared to a robot, and the pass-through picker space efficiency is improved by locating the storage cells opposite the storage device(s). As data storage products further progress, this limitation does not allow for the total number of storage cells to be maximized within the automated storage subsystem. Additionally, there is an ever increasing need to provide still greater amounts of storage capabilities in smaller spaces. Therefore, the pass-through picker in combination with the storage devices and storage cells should use space very efficiently.
Accomplishing increased storage capabilities in smaller spaces is enabled in part by improving magazine design. For instance, a magazine that minimizes its own area increases the amount of space available for cartridges and hence increases data capabilities. A storage subsystem using a pass-thru picker is further improved by using a pass-thru magazine which allows an operator to view cassette status, or remove and add cassettes during processing of other cassettes. A pass-thru magazine, however, presents additional design challenges including safety, the ability to hold cassettes for transport yet release those cassettes for processing and providing a visual status of processed and non-processed cassettes.
A solution for holding cassettes in a magazine type storage box while providing a means of a quick release of individual cassettes is described in U.S. Pat. No. 4,929,861 by Metcalf. Metcalf teaches the use of a bar having alternating openings and blockages having lock and release positions. The bar can be slid into a release position to make each of the plurality of cassettes releasable by positioning an opening below each lever and then depressing the lever to eject the cassette. Alternately, the bar can be slid into a locking position by situating the bar such that a blockage is below each lever thus preventing depression of the levers and thereby locking each cassette in its storage cell. Metcalf's design is directed towards a box for storing, and possibly locking cassettes therein to prevent theft. This design does not contemplate releasing all cassettes simultaneously for random access by a picker, nor does it provide pass-thru capabilities and import and export positions for cassettes. The storage box is not enabled for interface with an automated storage system.
A cassette magazine that addresses the issue of interfacing the magazine to an automated storage subsystem is described in U.S. Pat. No. 5,247,406 by Apple et al. Apple et al. teach a cassette magazine having cassettes that are freely removable by a picker mechanism by slanting the storage cells such that gravity holds the cartridges in place--a design that prohibits pass-thru storage. Additionally, a locking bar, separate from the magazine is relied upon to lock the cassettes in the magazine. The need for a locking bar is avoided in a design presented in U.S. Pat. No. 5,004,393 by Lunka et al., whereby a spring detent provides pressure sufficient to normally hold a cassette in the magazine yet weak enough for allowing a picker mechanism to remove the cassette therefrom. Releasably holding the cassettes in such a fashion is acceptable for transport since the magazine is not a pass-thru design and the cassettes can reliably rest against the closed end of the storage cells. However, given the weight of the cassettes and sufficient shaking of the magazine, cassettes could fall from the magazine resulting in damage to the cassettes.
An example of a cassette magazine that addresses the issues of providing pass-thru storage for cassettes is taught in U.S. Pat. No. 4,850,485 by Ishikawa. Ishikawa uses two stoppers, one on either side of a cassette, to releasably hold each cassette or lock all cassettes in the magazine. Ishikawa's design is complicated somewhat by the use of dual stoppers. The cassettes are not provided with import and export positions and the magazine is slid down into the storage subsystem such that magazine is held in place by gravity.
What is needed is a pass-thru cassette magazine having a single lock/releasable cassette holding mechanism wherein cassettes can be releasably and/or lockably held in either an import or export position, which lock mechanism interacts with the storage subsystem to interlock the magazine into the storage subsystem while releasably holding cassettes and alternatively to lockably hold such cassettes in either import or export positions when the pass-thru magazine is released from the storage subsystem.